Hmmm, the fusion case is rather nice, but it limits you in terms of upgrade functionality as the GPU can only be half height if you decide to upgrade. I went for the OcUK media case, simply as it avoids this issue. It won't fit particularly long cards due to PSU placement, but most medium spec cards aren't that long anyway.
I'd also consider looking at the Sandy (soon to be Ivy) based chips, as that way you've got a bit more CPU grunt for general usage, or for any rips which don't play nicely with your onboard decoding, or for potential future usage. You mention emulation, and that usually likes a decent processor, especially if you're looking at N64, GC, Wii etc. As an example Dolphin (Wii/GC) recommends a decent dual-core or better CPU
![Smile :) :)](/styles/default/xenforo/vbSmilies/Normal/smile.gif)
Do you already have a drive to use for the OS or are you planning to run everything of a 5400RPM drive?
You mention budget about £500, so here's one suggestion I threw together, you've got a small SSD so the OS and boot times are extremely snappy, a large low RPM media drive, BD, a I3 processor so a decent amount of CPU power and a moderately decent passive graphics card to minimise sound, without ruling out gaming. Throw in a few 120mm case fans of your choice and bobs your uncle.
For reference I've added an extra PSU despite one being included with the case, because it's a cheap, noisy thing, whereas Coolermaster have a good reputation when it comes to noise. The retail BD-RW should come with some BD playback software, usually Cyberlink PowerDVD9 or similar.
You could also be extra-luxurious and throw in something like this:
http://www.overclockers.co.uk/showproduct.php?prodid=KB-006-XB&groupid=702&catid=23&subcat=
Nice little keyboard/touchpad with media keys combo which should be perfect for a HTPC.